Seal Island rises from Encounter Bay's waters three kilometers west of Granite Island, a windswept granite outcrop that has served as a breeding ground for Australian fur seals since the species rebounded from near-extinction in the early twentieth century. Captain Matthew Flinders charted these waters in 1802 aboard HMS Investigator, naming Encounter Bay after his meeting with French explorer Nicolas Baudin the same week. The seals he observed were already scarce; by the 1830s, colonial sealing gangs had reduced the regional population to fewer than two hundred individuals. Legal protection arrived in 1891, and by the 1970s the colony had re-established itself on Seal Island's sheltered southern platform, where counts now exceed four hundred residents during peak breeding months. Victor Harbor seal island cruise tours depart from the Granite Island Causeway, a 630-meter stone bridge completed in 1875 to link the town with Granite Island's whale-watching lookouts. The causeway remains the only mainland connection to the embarkation point, and its horse-drawn tram—operational since 1894—still carries foot passengers alongside modern vehicular traffic. Cruise vessels navigate the channel between Granite Island and Wright Island before turning west into the open fetch of Encounter Bay, where swells from the Southern Ocean meet the shallow shelf that extends fifteen kilometers offshore. Water depth drops from twelve meters at the causeway to sixty meters at Seal Island's eastern face, creating upwelling currents that draw schools of pilchard and anchovy, the primary diet of both seals and the short-beaked common dolphins that hunt the same grounds. The island's granite formation dates to the Cambrian period, part of the same geological province that forms the Mount Lofty Ranges thirty kilometers inland. Wave action has carved sea caves into the island's southern and western flanks, providing haul-out platforms sheltered from prevailing southwesterly winds. Adult male fur seals occupy the exposed northern rocks, their territorial calls audible a kilometer downwind during the November-to-January breeding season. Females and juveniles cluster in the caves, where pups nurse for eight months before venturing into open water. Cruise vessels hold station twenty meters offshore—the minimum distance mandated by South Australia's Marine Mammal Protection Act—allowing passengers to observe nursing behavior, territorial displays, and the seals' distinctive porpoising swim style as they return from offshore feeding runs. Little penguins nest in Granite Island's boulder fields and occasionally raft near Seal Island during evening returns, while Australasian gannets and white-bellied sea eagles patrol the channel year-round.